Move Comes Amid Mixed Signals About Whether Assistance Is Legal

Merck & Co. and GlaxoSmithKline PLC are holding off on providing help with out-of-pocket drug costs to people insured under the Affordable Care Act, while other pharmaceutical companies go ahead, amid mixed signals about whether the copay assistance is legal.

The help is a staple of pharmaceutical-industry marketing to people insured by commercial health plans. It costs drug makers billions of dollars a year. But by subsidizing the out-of-pocket costs triggered by a prescription, companies can help to ensure that the...